 Okay, so yeah, I'll get started with thanking the organizers for giving me a great opportunity to attend this conference. I wish I could be there in person, but when I had to decide it was peak COVID period here, so I really decided not to travel that looking at the current situation, but now things are much better. So my talk today is about atomic force microscopy in liquids, looking at several interfacial phenomenon such as friction wear, lubrication, as well as tribochemistry which occurs under certain conditions if you have certain reactive molecules in the lubricants. So this is my current research group at IIT Delhi. A couple of students who did this work have graduated Prashant and Deepak and some of the work I will show was started actually at UPenn when I was doing my postdoc with Professor Karpik in collaboration with ExxonMobil. I'm continuing some of the work here. Apart from that there are many other areas I've started working on. For example, looking at injuring alloys and how the microstructure affects friction and wear at nanoscale. Lubricant additives interaction with some of the injuring alloys which I'll be mostly talking about today and apart from that I have started recently some work on silica glasses and looking at how to prevent scratching of these kind of glass materials and also I am collaborating with some experts in MD simulations to look at how 2D materials coatings on these glasses can prevent scratch and wear of these materials. I have also started some work on wear of 2D materials but this is very recent work we have just initiated and another project I've started recently is looking at biomimatic surfaces. I have a collaborator who makes these very interesting pattern surfaces so how we can control friction by tuning the interfacial structure by these nanopatterns is something also I'm very excited about but of course something I very recently started working on. So today I'll be focusing on tribology in liquids particularly focusing on industrial lubricant additives so the goal or the motivation is that we have huge amount of friction losses if you look at automotive engines for example around 16 to 17 percent energy total energy input is lost due to friction and it amounts to several hundred billion liters of fuel which is lost due to friction every year so even if we make small improvement in frictional losses we can save a lot of fuel as well as reduce emissions. So to control friction wear we use these additives which are added to the automotive lubricants which are interacting at the interface and are responsible for affecting friction and wear so how do we understand the interaction of these additives is very important. So this is the work which I initiated and I was at UPEN in collaboration with ExxonMobil so our journey started with looking at GDDP which is one of the most important lubricant additives which is added to automotive engine oil so what it does is that it interacts at the sliding interface between two rubbing surfaces such as piston ring and cylinder wall and the hypothesis is that some kind of chemical reaction happens at the interface because there is as pretty contact so there's high local pressure there's temperature and there's the reactive molecule which is compressed between these two surfaces but these two asperities but it's not clear what parameter really governs this reaction and how these films grow what is the kinetics of the growth and so on so we started looking at whether we can look at asperity level interaction of these additives so we used AFM as a tool so AFM as we know we can use it in liquids so but this is the first time we have used industrial lubricant additive GDDP in an AFM cell and using AFM we could do this test in a very localized area as shown here so we are looking at a specific region of interest and sliding the tip under this lubricant and then also we can change the temperature so by doing that we can see if this kind of tribal chemistry can be of where these reactive molecules are present so in this movie I show you the schematic of how by pressing at a very high pressure above a critical pressure can induce this growth of tribochemical film and then we can image this film by reducing the load and imaging a larger area so this is how we can quantify the volume of film growth or the amount of film growing on the surface and can measure the volume or the reaction rate as well by looking at how much volume is generated in a given time period so then we looked at various such as dependence on how this film growth is affected by contact pressure as well as temperature so this is a picture showing you how contact pressure increase is leading to faster growth of the film means we get higher thickness of the film as the pressure increases and if you continue to increase pressure you see a lot of deformation and damage of the film this is why you see very estimate features here because we are allowing the film we are damaging the film so when we look at how to explain this this travel film growth we use a very simple reaction rate theory and since we are looking at very we clearly that stress is affecting the reaction rate so we looked at how stress is affecting this reaction so by introducing the stress combining this activation volume we can see that if the stress is activating the reaction the energy barrier should reduce so by simply bringing the stress into this equation we can see whether this actually the simple model explains our result where stress activation can be taken into account as well as there's a temperature as a factor so what we did with AFM is that we independently varied stress and then in a separate experiment we make we maintain a fixed contact load and varied the temperature in that way we can verify whether this simple model works to explain our results so we looked at the growth rate of the film which is calculating the volume and dividing by time so we can calculate how much of volume is growth growth occurs per second and then looking at how this growth rate is affected by contact pressure so we see that there is a very nice fit to the data up to certain point beyond that this fitting doesn't work and the reason for that is that up to this pressure where this fit works we see that the film growth occurs without any significant damage to the tribo film but beyond a critical value lot of deformation of the film happens so this this fitting doesn't work because now you are damaging the film so the growth is not continuously increasing with pressure it is saturating due to wear of the film so in another experiment we varied the temperature independently and we see that for a given pressure if we vary the temperature again there is an exponential increase in growth rate of the film as the temperature increases and again we verified that the film growth is actually increasing with temperature by directly in situ imaging the tribo film and we get very similar Delta G values from what we got from previous experiment where stress was varied so this confirms that our simple model which is suggesting that there is a chemical reaction tribo chemical reaction and it can be monitored and this is an industrial molecule which we are trying to see at the asperity level so this was quite exciting and then several people asked us whether this will be observed only at asperity level or this is this can be seen in multi asperity contact as well so so far most of the tribology experiments previously were done using tribometers which is a multi asperity instrument but there is no in situ imaging capability in those instruments so what we did was we modified the AFM probe we mounted a steel microsphere and then by doing that we could generate a multi asperity contact and the advantage here is that this becomes like a tribometer kind of ball and disc instrument and in addition you can do simultaneous imaging also because you can track the deflection of the cantilever very precisely so by doing that we could do similar test with a multi asperity contact using steel and substrate also instead of simple silicon or iron film we took an actual steel surface so here is a movie which shows the steel microsphere sliding on a steel substrate and as I said the advantage is that you can in situ observe the triboplin growth so you can see that the triboplin growth is observed here and simultaneously we are measuring friction as well as the thickness of the film as well as if anywhere is happening all these things can be monitored at the same time without taking the sample out of the system and friction versus load followed very nice linear relation so we could measure the friction coefficient as well and we could track in different regions in terms of variability and looking at triboplin characteristics whether it varies from one experiment to the other and by as I said we can image the triboplin we can zoom out and take an image where the sliding test was done and we can clearly see a build up of a film which is 5200 nanometer thick and it looks very similar to what we observed in single aspirated test in addition the parameters which were used to grow this film in terms of temperature was the same so we in our test we never observed these terms forming at room temperature which means that you need elevated temperature whether it is single aspect or multi aspect as well as you need high contact pressure of course in multi aspect test we cannot precisely say what kind of pressures are there because there's multiple contacts occurring but on average we can have some estimate of that so now after this we started looking at at IT Delhi my students we collaborated with the group who are experts in this aluminium and magnesium alloys so we started looking at real injuring alloys because these are used for automotive engine components so here the primary phases are basically the aluminium matrix and silicon phase so this alloy is very important for a tribological applications especially for engine components and the the growth mechanisms of ZDDP film has been studied on these alloys for decades but there's a lot of debate because some people say there's formation of the film on aluminium matrix some people say there's there's no film growth observed in certain experiments so we try to do this in-situ study and we did a simultaneous sliding test on these two regions aluminium and silicon alloys silicon phase so in a simultaneous sliding we could directly observe whether this film is forming or not and our test showed that actually film is forming on both regions but when we did a careful analysis we found that there is some difference so here is a region you can see that the silicon phase aluminium matrix around it region 2 and 3 we look at the thickness of the film the thickness of the film on aluminium matrix was significantly lower compared to silicon phase and also the film was very rough which means this is more patchy compared to silicon phase where the film is more dense you can see the roughness of the film is much lower another test we did that we did a sliding test away from the silicon phase where there's no silicon region only aluminium matrix and we saw that there's significant wear of the aluminium starts before we form any material so this was very strange to observe because we see aluminium matrix which is next to silicon it shows tribo film growth and much lower friction but aluminium matrix where we are sliding away from the silicon phase we see very high friction and we don't hardly see any tribo film formation so we did a lot of indentation test and we found that there's no difference in hardness of aluminium very close to the silicon versus away from silicon so aluminium matrix properties are not very different so what we believe is that this silicon phase is very hard so that's where contact pressure is high and tribo film formation starts much easily because it's activating the reaction and this is allowing us generation of lot of these reactive species which are easily transferred to the surrounding region when we are doing a sliding test and before we induce wear of aluminium this species bind to the aluminium and form this film whereas in this case there is no easy activation of the reaction initiation of the reaction and before that reaction activation or initiation happens the matrix where starts to happen before that and we start to wear away the material so this is our hypothesis but there's no direct evidence and let's do some theoretical study so we try to see if we could minimize the wear of this aluminium matrix so what we did is that we did a collaborative study with Indian Institute of Petroleum where they are growing or they are forming this hexagonal boron nitride nano sheets which can be dispersed by some functionalization in lubricant and we combined it with this ZEDP containing lubricant we see that these are small nanoparticles of HBN so when we added that to the lubricant we found that the tribo film whether you see close to the silicon phase on aluminium or away from the silicon hello hello so Anita could you try to come closer to your conclusions yeah yeah so so this is where we see that there's a lot of significant reduction in wear of aluminium matrix and also we see that it correlates well with the friction data that we see much lower friction when we have very low wear of the matrix so this is significantly lower friction compared to what we saw when there was a wear of the aluminium matrix and we also found that the the HBN nano sheets they bind strongly to the tip you see the signature of nitrogen and boron near the contact zone which is somewhere here and also there's some adsorbed molecules also this is why we are seeing signals corresponding to other ZEDP molecule in other regions as well but close to the contact we clearly see strong nitrogen and boron signal which means this is reducing the friction as well as wear of the lubricant of the overall system so next study is on magnesium alloys but I will not present it due to lack of time I thought I had 25 minutes but seems like we are running late so I'll stop here if you're interested you can refer to this paper in advanced engineering materials which we published on magnesium alloys where we looked at effect of microstructure on this interaction of lubricant additives with magnesium alloys and this was the first study on magnesium alloys or aluminium alloys at nano scale using this technique so we are trying to see if we can understand real engineering systems and interaction of real industrial lubricant additives at nano scale with these important alloys that can give us very useful information which can be useful for various industrial applications as well as for scientific understanding of these important materials so yeah I will not go through magnesium alloys results the conclusion is again it's a new approach which we demonstrate and we can study lubricant additives on real engineering alloys and look at the effect of microstructure quite well with this approach with this I would like to acknowledge my previous collaborators my previous advisor put a perfect and Exxon Mobile colleagues my current collaborators my funding agencies and I would also like to highlight that we are organizing a tribology conference in New Delhi in December this year so you all are invited if you have time and interest to travel to India there's a lot of tourist attractions nearby so I think there's a lot of motivation to travel if you have if you can manage yeah with this I would like to thank you for your time and thank you very much thank you very much thank you work yeah okay thank you very much very interesting talk so as you shown the type of substrate really influences the tribal film growth so I was just wondering the type of tip used for the very first experiment you showed was he still and also what is the model lubricant you use what is the kind of oil thanks you mean the multi-asperity contact or single asperity contact yeah multi-asperity contact okay so so first one we had so that was done in UPenn and this was a company called nano steel they provide steel very high hardness steel micro sphere which is used for sand blasting so these micro spheres of steels were attached to the cancellable but later on the studies I did I try to eliminate iron because there's a lot of controversy about iron catalyzing the tribochemical reaction so I try to eliminate iron in later studies which was done on nonferrous alloys like aluminium and silicon aluminium silicon and magnesium alloys so I used an alumina probe so this alumina probes are ultra smooth nanometer or a couple of nanometer rough these are alumina probes so there's no iron in the system so to eliminate iron I use those alumina probes later on and I still see ZDDP tribofilm forming when there's no iron at all in the system but it and also it forms where the contact stresses are high like these precipitates of magnesium aluminium alloy MG17 AL12 and also the silicon precipitates in aluminium silicon alloys these are hard precipitates so there we see this film formation very occurring very readily whereas the soft alloy soft phases around the precipitate they undergo wear unless we tried this addition of HBN to the lubricant it showed some promising results that some reduction of the soft matrix can be achieved by tweaking with the chemistry of the lubricant and what was the oil sorry what was the oil that you use what was the oil so the base oil is we use two types of oil one is PA04 polyalpha aliphant 4 and it there's another oil group to base oil it's called Mac 65 which is which we obtain here from one of the industry so these are standard base oils which are used in automotive engine lubricants so PA04 is more standard it's globally available I think even in UPEN I was using that from X1 mobile they provided us that it is available here as well so we can use it is the same usually it's very inert we don't see anything happening if we just use the base oil no reaction nothing so so it's quite we are confident that that is not affecting any of the results okay especially the tribo film formation there is a question from the remote yes I hope the connection works did you see any correlation of the stiffness of the films depending on the stiffness of the substrate or did you not look at the stillness of the phosphate I have so far not started looking at it because it's very very tricky to measure because what happens when you try to measure mechanical properties of these films the tip picks up something and you get all sorts of reasons so so yeah it is something which is what we want to do in future but so far we have not quantified the mechanical properties of the tribo but it's it's very important and I believe especially in aluminum silicon alloy we see that thickness and roughness of the film is very different in the neighboring regions so that's where we should expect a lot of difference in the mechanical property as well as chemical property but that is even more challenging to quantify because it's such a small area how will we quantify chemical information with good decision I'm not sure thank you okay with that we thank Nitya Goswami very much thank you the last